1. Field of the Invention
This invention relates to the field of vacuum filters. More specifically, this invention relates to the field of drum lime mud filters and an apparatus to improve cleaning and efficiency thereof.
2. Prior Art
Lime mud filtering has been known for a substantial number of years and drum type filters have been favored for many years as well. Due to the extensive interest in this field, many modifications and other devices have been invented and employed with lime mud drum filters. One such arrangement has been proposed by Esko Mattelmaki in U.S. Pat. No. 5,149,448. '448 discloses a drum filter for thickening lime sludge in which the lime sludge is thickened on a filter layer having a precoat formed of the lime sludge itself. The device is also provided with high pressure liquid nozzles which continuously reciprocate in the longitudinal direction of the drum. The nozzles are located under the doctor blade on the descending side of the drum. The reference teaches to mount two high pressure nozzles in that location in such a way that one of the nozzles breaks the precoat so that it drops into the vat and that the other nozzle washes the filter cloth clean. While the device does clean the filter it suffers from the drawback of increased wear on the filter medium due to unnecessary overcleaning of the filter element. Moreover, the device of the prior art requires a long cleaning time and, therefore, accelerates motor and drive mechanism wear.
Another prior art device is disclosed in U.S. Pat. No. 5,470,472 to Baird et al. The disclosure teaches a non-traversing cleaning mechanism located on the descending side of the filter drum. Baird et al. teaches that the jets should be angled with respect to the filter media by selecting an angle of from 0 to 45 degrees and more preferably from 0 to 30 degrees measured from a vertical reference.